Flexible waveguides with 45° corrugations to allow bending and twisting of waveguides

ABSTRACT

A flexible waveguide (1) has corrugated seamless walls (2) the corrugations of which are inclined to the transverse planes of the waveguide, that is, planes perpendicular to the longitudinal axis of the waveguide, at an angle of substantially 45°. The inclined corrugations, which may be annular or helical, permit both flexing and twisting of the waveguide.

This invention relates to flexible waveguides.

PRIOR ART

A known construction of flexible waveguide has walls which have acorrugated or bellows-like conformation, the corrugations lying inplanes transverse to the longitudinal axis of the waveguide. Thecorrugations may be formed by winding a conductive metal strip such asbrass and sealing adjacent windings together by solder. Such a waveguideis flexible by virtue of the flexibility of the strip forming theindividual corrugations, but is not in general capable of being twisted.In order to sustain an angular deformation or twist about itslongitudinal axis a corrugated waveguide has to be formed withinterlocking corrugations which overlap, for example, around a wire corewhich is wrapped around the waveguide; sliding movement of theindividual corrugations or "turns" relative to the wire core permits adegree of twist in the waveguide.

BRIEF SUMMARY OF THE INVENTION

The present invention seeks to provide, in a simple construction, acorrugated waveguide which is capable of sustaining both bending andtwisting movements.

According to the invention there is provided a flexible waveguide havingcorrugated walls the corrugations of which are inclined to thetransverse planes of the waveguide, that is, planes perpendicular to thelongitudinal axis of the waveguide at an angle of substantially 45°.Such a corrugation angle has been found in practice to permit combinedbending and twisting of the waveguide.

Upon flexing of the waveguide according to the invention the waveguidecan exhibit both bending and twisting deformation. Such deformation canbe useful for certain interfacing applications. In some cases the degreeof twist imparted to a length of the flexible waveguide will be a resultof a bending of the waveguide and will depend on the exact angle of theinclined corrugations, the length of the waveguide and the degree ofbending imparted thereto. In other cases, bending and twistingdeformations of the waveguide will be independent of each other.

The corrugations in the waveguide may be rectangular in cross sectionalprofile. Alternatively the corrugations may have a substantiallysinusoidal cross sectional profile, applicable more particularly to thelarger sizes of waveguide.

The waveguide according to the invention is preferably seamless. Thecorrugations may be obtained by, for example, an hydraulic cold-formingprocess or an electro-forming process.

The seamless flexible waveguide according to preferred embodiments ofthe invention, in contrast with previously known twistable waveguides,does not have any discontinuity between adjacent corrugations, forpermitting relative sliding movement between these corrugations. Sincethe corrugations are formed in a single piece of sheet metal withoutdiscontinuity the degree of radio frequency leakage exhibited by theflexible waveguide according to the invention is potentially less thanthat exhibited by flexible waveguides of the traditional constructionreferred to previously.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The invention will be further described, by way of example only, withreference to the accompanying purely diagrammatic drawings, in which:

FIGS. 1 to 4 are respective plan views of sections of flexible waveguideaccording to four different embodiments of the invention,

FIG. 5 is a perspective view of part of the flexible waveguideillustrated in FIG. 3 with annular corrugations, illustrating itsflexing and twisting characteristics, and

FIG. 6 is a perspective view of part of the flexible waveguideillustrated FIG. 3 with multi-start helical corrugations, showing itsflexing and twisting.

DETAILED DESCRIPTION

FIGS. 1 to 4 illustrate sections of flexible waveguide 1 the walls ofwhich are continuous, that is, seamless, and formed with corrugations 2which are inclined at an angle α of substantially 45° to thelongitudinal axis of the waveguide 1. In other words, the corrugations 2are inclined at 45° to the transverse planes in which the corrugationsof a conventional flexible waveguide would normally lie.

The corrugations 2 in the waveguide are preferably of helical or spiralconfiguration, as illustrated diagrammatically in FIGS. 1 and 2respectively, with a pitch angle α of 45°. Alternatively, thecorrugations 2 may be fully annular, as illustrated in FIGS. 3 and 4.where the corrugations 2 are of helical form, the requisite corrugationpitch is achieved by conforming the corrugations to a multi-starthelical configuration.

The individual corrugations, whether of spiral or annular form, may havea rectangular

profile, as illustrated in FIGS. 1 and 3. Such corrugations areparticularly applicable to the smaller sizes of waveguide down tomillimetric sizes and are readily formed by electroforming techniques,that is, by electrolytic deposition of the waveguide upon a former orarbor, which is subsequently dissolved.

The corrugations 2 of the waveguide may alternatively have a generallycurved cross sectional profile, for example the sinusoidal profileillustrated diagrammatically in FIGS. 2 and 4. Corrugations of thisprofile are readily formed by hydraulic deformation of an initiallysmooth wall waveguide to conform to a profile determined by an externaldie or mould, the waveguide walls being deformed by the application ofan internal hydraulic pressure. Corrugations of this profile aresuitable for waveguides of larger sizes up to 26 GHz.

It will be understood that in practice the electroforming process mayalso be used for the production of waveguides of the kind illustrated inFIGS. 2 and 4, and the hydraulic forming method may be used forwaveguides of the kind illustrated in FIGS. 1 and 3.

The inclined corrugations 2 of the flexible waveguide according to theinvention permit flexing and twisting deformation of a section ofwaveguide, as illustrated schematically in FIG. 5 and FIG. 6. Theinclined corrugations allow normal flexing of the waveguideperpendicular to its major face, as indicated in broken outline in FIG.5 and FIG. 6, and also a twisting deformation of the waveguide, as shownin full outline the waveguide shown in FIG. 5 has annular corrugationsof rectangular profile inclined to the longitudinal direction of thewaveguide, whereas the waveguide shown in FIG. 6 has multi-start helicalcorrugations of rectangular profile.

In the illustrated embodiment, the flexing of the sections of waveguide1 and 11 is indicated by the arrow F and is accompanied by a twistingdeformation indicated by the arrow T. It will be seen that as a resultof the bending and twisting of the waveguide the opposite ends of theflexed section of waveguide, as well as lying in different planes as aresult of the bending of the waveguide, are also angularly displacedrelative to each other about the longitudinal axis of the waveguide.

The degree of twisting may be predetermined, for a given length ofwaveguide, by the degree of bending imparted to the waveguide, or may becompletely independent of the flexing of the waveguide.

The invention has been described in its particular application toflexible waveguides of rectangular cross section; it will be understood,however, that the invention is also applicable to flexible waveguides ofcircular and other cross-sectional profiles.

What is claimed is:
 1. A waveguide capable of being bent and twistedthrough substantial angles, and formed of discontinuity-free metaltubing with continuous corrugations of the wall of the waveguideextending all around the waveguide at an angle of substantially 45° tothe longitudinal direction of the waveguide.
 2. A flexible waveguideaccording to claim 1, characterised in that the corrugations have arectangular transverse profile.
 3. A flexible waveguide according toclaim 1, characterised in that the corrugations have a substantiallysinusoidal transverse profile.
 4. A waveguide according to claim 1having substantially circular cross-section wherein the corrugations arecontinuous multi-start interwound helical corrugations at an angle ofsubstantially 45° to the longitudinal direction of the waveguide.
 5. Awaveguide according to claim 1 having substantially rectangularcross-section wherein the corrugations are continuous multi-startinterwound helical corrugations at an angle of substantially 45° to thelongitudinal direction of the waveguide.
 6. A waveguide according toclaim 1 having substantially rectangular cross-section wherein thecorrugations are oblique continuous annular corrugations in which theindividual corrugations on each wall of the waveguide are at an angle ofsubstantially 45° to the longitudinal direction of the waveguide.
 7. Awaveguide capable of being bent and twisted through substantial anglesand consisting of seamless metal tubing with continuous multi-startinterwound helical corrugations at an angle of substantially 45° to thelongitudinal direction of the waveguide.
 8. A flexible waveguideaccording to claim 7, characterised in that the corrugations have arectangular transverse profile.
 9. A flexible waveguide according toclaim 7, characterised in that the corrugations have a substantiallysinusoidal transverse profile.